Bypass switch for RF networks

ABSTRACT

A make-before-break bypass switch is combined with a pair of probes projecting from a support where a member is provided with sockets to slidably receive the probes. The probes define a gap in a first RF circuit. The corresponding sockets are connected by a second RF circuit. A pair of spring clips on the support are connected by a bypass circuit on the support and are designed on retraction of the sockets from the probes to connect a bypass circuit between the probes before the sockets are completely disconnected from the probes. On application of the sockets, the sockets are designed to connect to the probes before a part of the member disconnects the spring clips from the probe. If the first RF circuit may carry signals in either direction and the second RF circuit is directional, the probes and sockets may be arranged to allow reversal of the sockets relative to the probes.

This application is a continuation of application Ser. No. 08/426,232filed Apr. 21, 1995.

This invention relates to improvements in circuitry and the physicalarrangement thereby for use in a housing for coaxial cable distributionnetworks. By the term `coaxial cable distribution networks`, I includeCommunity Antenna Television (CATV) networks, Local Area (LAN) Networks,and other coaxial applications, including those carrying telephonesignals particularly those which require broad-band transmission.

In general the invention described herein may be usefully consideredagainst the background of the components described in the followingparagraph. However the individual inventions are believed to haveapplications in radio frequency (`RF`)circuitry beyond the applicationin the following paragraphs. The circuitry herein is designed for RFsignals of 5 Megahertz to 1 Gigahertz but is useful at higher and lowerfrequencies than this range.

BACKGROUND OF THE INVENTION

The background arrangement of components includes a conducting housingwhich has in one wall a common port CP and a pedestal port PP forrespective connection to coaxial distribution cable, sometimes known as`hard line` and in the opposed wall of the housing has an aerial port APfor similar connection. The invention however also applies to`dedicated` two-port housings having only a common port and either anaerial or a pedestal port. A plate of insulating material, of the typecommonly called a `motherboard`, carries RF and alternating current(`AC`) circuitry and supports and is connected to the RF circuitry(commonly a coupler and splitter), for connection to customer ports,also known as `secondary` or tap ports. There is an RF through path onthe motherboard which is connectable at one end to the pin of thecoaxial cable which is at the common port. The other end of the RF pathon the motherboard is connectable to either the centre pin of a coaxialgable connected to the aerial port or the centre pin of a coaxialconductor connected to the pedestal port. An AC path (since the coaxialcable typically carries RF and AC) typically diverges from the RF topass through an inductor adjacent one end of such path and joins itagain, near the other end of the RF path. The RF path (unless bypassed)connects to active or passive RF circuitry. Typical of the passivecircuitry is a coupler and splitter for providing RF signals to the tapports. The coupler is designed to operate on RF signals in only onedirection in the path. Hence when, as is later discussed, the RF paththrough the housing is reversed, means must be provided for reversingthe coupler relative to the remainder of the RF through line. Thehousing is usually one of a number connected in series with others atspaced intervals along lengths of coaxial cable forming part of thedistribution network. It is undesireable if an RF through path isinterrupted in one housing since it interrupts the reception ofcustomers downstream in the distribution network. Bypass means aretherefore provided if the coupler is removed.

GENERAL DISCUSSION OF INVENTIONS

The inventive features are discussed against the background of thepreceding paragraph. However they can, at least to the extent discussedhereafter, be used in other environments than those discussed therein.

In one facet of the invention a novel terminal is provided forconnection, on the one hand to the RF through circuit inside the housingand on the other hand to the centre pin of a coaxial conductor connectedto one of the ports AP, PP or CP. (Typically such terminal will be usedat each port). The `centre pin` of a coaxial cable is used herein toinclude conventionally used additions or extensions to the coaxialcentral conductor, per se. The outer coaxial conductor is provided witha threaded nut, which is screwed on complementary threading on theoutside wall of the housing, about the port. This has the effect ofestablishing an electrical connection between the outer coaxialconductor and the conducting housing while carrying the projecting endof the centre pin into the inside of the housing for contact with theterminal to be described. (The housing is open topped and closed by alid). The terminal comprises a pair of opposed contact members (only oneneed be conducting although preferably both are) biassed toward eachother to a closer spacing than the diameter of the centre pin andrelatively movable against said bias to spacing greater than saiddiameter. The approximate path of relative movement of the contacts toeach other is transverse to the insertion-withdrawal direction of thepin and transverse to the withdrawal or insertion direction of theterminal and attached components into and out of the housing.

The opposed contacts are aligned with the entry-withdrawal direction ofthe pin and provided with deflecting surfaces so that entry of the pininto the casing as a part of the attachment of a coaxial cable to theport, causes the pin to move the opposed contacts apart, so that, underthe bias, they grip the pin between them, establishing electricalcontact between pin and terminal. When the coaxial conductor iswithdrawn from the port, the pin may slide out from between the contactsto allow them to assume their minimum spacing.

It is important to note that the cable may be attached and detached fromthe housing, making and breaking electrical contact between the pin andthe terminal, without disturbing the circuitry inside the housing whichis connected to the terminal contacts. In fact the pin and coaxialconductor may be withdrawn without opening the housing.

To attach the terminal contacts to the pin, means are provided foroperation inside the open housing to spread the contacts, against thebias, to a spacing wider than the central pin diameter. At suchdeflection, the terminal and any components physically attached theretomay be moved toward the pin in a direction transverse to the pin, and tothe relative direction of relative movement of the arms so that thecontacts may be located on each side of the central pin. In thisposition, the means spreading the deflecting means may be releasedallowing the contacts to grip the pin and make electrical contacttherewith With a pair of contacts already gripping the pins thespreading of the contacts allows removal of the terminal and anyequipment attached thereto from the housing--straight upwardly out ofthe casing, without disturbing the pin, which remains in place.Conversely, with the pin in place, and the terminal and its attachedcomponents, out of the housing, the spreader may be used to spread thecontacts and the terminal and its attached equipment lowered into placewith the contacts straddling the pin, so that the spreading means may bereleased to allow the arms or contacts to grip the terminal and makeelectrical contact.

It should be noted that the terminal may be removed from and replaced onthe pin without detachment or disturbance of the pin or coaxial cable.

It should be noted that it is within the scope of the invention todesign the opposed contacts and their biasses with guide surfacesoperable on relative movement transverse to the pin and the biasdirection so that they may be removed or removed and replaced from theterminal without the necessity of using the spreader.

In accord with another aspect of the invention an insulating plate ormotherboard is provided for mounting in the housing and the RF throughcircuit is mounted thereon. The plate is commonly a flat thin layer ofwhat is commonly known as printed circuit board (`PCB`). The plate is aninsulator and is commonly constructed of a mixture of fibreglass andepoxy resin but may have different constituents and may be madeinsulating material such as molded plastic, cardboard or paperboard.Such insulating plates have a dielectric constant dependant on thematerial making up the plate. At the RF signal frequencies in the RFthrough circuit the RF signal strength dissipated in the plate will varyas the dielectric constant. The circuitry and associated components aredesigned to lessen such losses.

The RF frequencies' signals in the RF through path tend to interact withthe conducting housing to produce eddy currents and standing waves inthe housing. Such eddy currents and standing waves result in the loss ofRF signal strength. It is of considerable importance to design theinsulating plate and other RF circuit components described herein, toreduce the strength and incidence of such eddy currents and standingwaves.

Accordingly, considerable design features are provided herein to reducedependance on the dielectric qualities of the PCB and in reducingtendencies of the RF circuit or its physical environment to createcurrents in the housing.

The insulating plate customarily mounts the terminals for the common andpedestal ports and mounts or is connected to the terminal for the aerialports.

The insulating plate provides the insulating support for the throughportion of the RF circuit. The through line of the RF circuit is thatportion which enters the housing at the upstream end (relative to signalflow in the coaxial distribution cable) and leaves at the downstreamend. (It should be remembered that the housing and contained componentsare designed for signal flow in either direction through the RF throughline).

In contrast to the through line there will be branch circuitrycharacteristic of that housing which will be normally connected to thethrough line. Most commonly the branch circuitry will comprise a couplerand splitter, for providing subscriber signals at the secondary or tapterminals. The presence and characteristics of the coupler and splitterhave effects on the design of the inventions discussed. It will be notedthat the coupler is undirectional. Hence its connections to the RFthrough line must be reversed if the RF signal direction along thethrough line is reversed. Moreover interaction between the signals ofthe branch RF lines and that of the through line must be reduced as faras possible as must currents in the housing due to branch line RFsignals.

The coupler is directional and carries the RF main feed between RF mainfeed input and the RF main feed output terminals. The coupler furtherprovides a tap output usually connected to the input of a splitter.When, in this invention, the coupler is installed, the couplerconnection and components are connected between the main feed input andoutput terminals, they form part of the RF through path in the housing.The tap output does not. In accord with a preferred embodiment of theinvention, when the coupler circuit is removed, the RF through pathbypasses the coupler main feed input and output terminals.

Thus one end of the RF through line is connected to the terminal for thecommon port and the other end of the through line is connected to means,preferably a transfer switch, mounted on the insulating plate forselectively connecting the RF through line either to the terminalassociated with the pedestal port or to the terminal associated with theaerial port. In this context the terminals are preferably, but notnecessarily, in the form of the novel terminal described herein.

The transfer switch is preferably of the type having a rotary controlknob. At 90° intervals about the axis of rotation, four terminals areprovided. The transfer switch is designed to have a pair of bridgingbars each having two positions and at each position adapted to connect adifferent pair of the four terminals.

The transfer switch has four fixed contacts. One is connected to the endof the RF through line opposite to the end connected to the pin at thecommon port. The opposed contact is connected to ground through aresistor intended to have an impedance characteristic of the coaxialtransmission line connected to the pedestal or aerial port. The otheropposed contacts are respectively connected to the aerial and pedestalports.

Thus in one position of the switch the end of the RF through path remotefrom the common port is connected by one bridge of the switch to theaerial port while the other bridge of the switch connects the (thenunused) pedestal port to ground through the characteristic impedanceresistor. In the other position of the switch the RF line is connectedto the pedestal terminal and the aerial terminal is connected to thecharacteristic impedance resistor. The connection of the unused terminalto the housing reduces the incidence of harmonic or resonance effects inthe otherwise unconnected lines particularly of such effects at suchfrequencies as will correspond to or interact with RF signalfrequencies.

The RF through line path across the insulating plate will tend to causestanding waves and eddy currents in the housing. To reduce such effectsa first ground plane usually in the form of metal foil, located on theside of the insulating plate facing the housing, follows the RF throughline circuit as far as possible across the plate. Thus the first groundplane is connected to the conducting housing adjacent the connection ofthe common port pin to its plate terminal. The ground plane contour thenfollows, at a determined spacing, the RF through path across the plateto a further connection to a housing wall adjacent to the point wherethe other end of the RF through path connects to the RF signal linebeyond the boundaries of the insulating plate. The design effect is toprovide that the impedance between the ground plane and adjacentportions of the RF through path which it accompanies, approximates thecharacteristic impedance. In this way interaction of the RF signal withthe housing and the signal losses due to reflections and standing wavesin the housing are greatly reduced.

In a preferred embodiment the first insulating plate also provides acoupler tap RF signal path from the coupler to the splitter input. Asecond insulating plate ground plane is contoured to accompany thetap-splitter signal path at approximately the characteristic impedancespacing. The second insulating plane is also contoured and located toreduce interaction between RF through line path signals and thetap-splitter path signals to reduce signal loss in either path due tothe presence of the other. This particularly benefits the strength andintegrity of the signal on the tap-splitter path in view of its largeattenuation relative to the signal strength on the through path.

In some cases it is found that losses due to ground plane resonance aregreatly reduced if the two ground planes are combined and strip TZ isconducting foil, joining ground planes GP1 and GP2 (FIG. 5).

The coaxial cables carrying signals to and from the housing; typicallyalso carry alternating current (`AC`). There is therefore provided an ACbypass circuit, bypassing the RF through line interfaces with thecoupler circuit. The AC and RF circuitry an specifically designed toreduce, to tolerable amounts, the AC in the RF circuitry and vice versa.

The CP and PP terminals are preferably mounted on the insulating plateas is the branch RF circuitry.

The insulating plate: with terminals, RF through line, AC bypass,transfer switch and mounting for the coupler and splitter; forms aplatform or part of it which maybe removed and replaced in the housingas a unit, thus reducing the `downtime` caused by such repairs orreplacements and reducing the interruption of service, not only to thesubscribers served by connection to that housing but also to thesubscribers downstream along the exit coaxial distribution line.

In the housing of generally square shape presently conventionally usedthe insulating plate will essentially be the platform, which may beremoved and retained or replaced.

There has however come a need for a longer housing. When a housing whichis connected to upstream and downstream distribution lines, has to bereplaced, quite frequently the only practical way, is for the repairmanto cut the coaxial cable on each side of the housing, adapt the cableends for reattachment, and connect to the new housing. The shortening ofthe cable lengths renders them difficult to attach to the new housing.Accordingly, there has arisen the need for a longer box. With the commonand aerial ports at opposite ends of what is generally a rectangularhousing, an internal transmission line is required from the motherboardto the aerial terminal. This transmission line may be an internal (tothe housing) coaxial line but the need for support for the centralconductor introduces losses between the internal line central andoutside conductors.

A trough line, where the outer conductor only partially encloses theinner allows an `air line` where, except adjacent the ends, there isnothing but air between the conductors along the length. Whatever theinternal transmission line used, the connection from the aerial portterminal to the motherboard including the internal transmission line ispreferably rigidly connected to the insulating plate, forming, withinthe long housing, a part of the platform, including the motherboard, forremoval from or replacement in the housing, as a unit.

Although the bypass switch is used herein to bypass the coupler circuitas part of the RF through line, the bypass switch may be used in otherRF circuitry than that specifically described herein.

In accord with this aspect of the invention, two probes for connectingthe RF through the coupler interface circuitry, are located on themotherboard. In accord with well known coupler design the couplercircuitry requires one probe for an RF (through line) input and theother probe for an RF through line output. (These probes are in additionto additional probes including an output to the splitter.) In accordwith a preferred aspect of the invention the coupler circuitry ismounted on insulated plate preferably of the same constituency as thefirst. The second plate is sometimes called a `daughter board` and isseparable from but mounted on the motherboard.

The first insulating plate mounts a row of upstanding probescorresponding to the through line, accessory and splitter connectionsrequired. The RF through line probes are at each end of the row. Thesecond plate mounts a complementary pat tern of sockets which may bemoved as a unit onto the probes. As the second insulating plateapproaches the probes, the RF first insulating plate end probeselectrically connect to the corresponding end (RF through path) socketsmounted on the second insulating plate, a certain distance fromcompletely assembled position. On movement away from assembled positionthe RF through line probes and sockets of the two boards break contactat the same certain distance. With the second insulating plate removedfrom the first, two spring contacts the first plate make respectivecontact with the RF through line probes. These spring contacts areconnected to a conductor the first plate which bypasses the RF probesand has the effect, when connected to the RF through line probes, ofcompleting the RF through line along the bypass thus ensuring carryingof the RF signal to housings and their subscribers downstream from thehousing in question, even though the second insulating plate is absent.

The second insulating plate is provided with insulating members whichmove with the second plate sockets toward and away from the first plate.These insulating members are located and dimensioned to make or breakelectrical contact between the spring contacts and the RF through lineprobes at a point closer in the member spacing from completely assembledposition, than the make break-point between the probes and sockets. Thuson relative separating motion of the second plate, the bypass connectionfor the RF motherboard circuit is completed before the RF connection tothe daughter board is broken. On relative assembly movement, the RFconnection to the daughter board is made before the bypass connection isbroken. Thus whether the second plate connection is being completed orinterrupted the RF through line is never disconnected and service todownstream housings and end users is not interrupted during removal ofthe second plate.

BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which illustrate a preferred embodiment of the invention:

FIGS. 1 and 2 show housings in accord with the invention, with lidsapplied, on aerial and pedestal mounts, respectively,

FIG. 3 is an exploded view of the housing showing the platform and thegeneral arrangements of the components mounted thereon, but omitting theelectrical connections and paths,

FIG. 4 is a plan view of the housing with platform attached but omittingthe electrical connections,

FIG. 5 is a plan view of the motherboard and the electrical connectionsthereon but with the transfer switch rotary marker removed. However thedrawing convention used in FIG. 5 differs from that of the otherdrawings in that components below the motherboard are shown in solidlines and components above the motherboard are shown in chain dot. (Inthe remaining Figures the usual convention is used so that components`visible` to the viewer are shown in solid lines and components hiddenfrom the viewer are shown as chain dotted or dotted),

FIGS. 6 and 7 are plan views showing the platform circuit with thetransfer switch positioned for pedestal and aerial mount, respectively,

FIGS. 8A, 8B and 8C show the construction of terminal for use at theaerial port,

FIGS. 9A and 9B demonstrate the construction of a terminal for use atthe common or pedestal ports,

FIGS. 10A and 10B demonstrate the trough line mounting adjacent theaerial port,

FIGS. 11A, 11B and 11C are vertical sectional views demonstrating theoperation of a terminal,

FIGS. 12A, 12B and 12C are horizontal sectional views demonstrating theoperation of a terminal,

FIGS. 13 and 14 demonstrate the operation of the make before breakswitch,

FIGS. 15A and 15B show side and top views, respectively, of the bypasscircuit,

FIG. 16 shows the schematic arrangement of the daughter boarddirectional coupler circuit,

FIG. 17 is a perspective view of the transfer switch,

FIG. 18 is a sectional view of the transfer switch,

FIGS. 19 and 20 are top views of the transfer switch, indicating itspositioning for pedestal and aerial mount respectively,

FIG. 21 is a partially schematic view of the trough line,

FIG. 22 is a perspective view of the outline of the trough line,

FIG. 23 demonstrates an alternative construction for conductors on themotherboard.

In the drawings is shown a `long` housing 10 of generally rectangularshape having opposed end and side walls 14 and 16, respectively, (seeFIG. 3) and four bosses 12 for lid 16 attachment by bolts (see FIG. 1).The housing is generally rectangular and has ports as now described inthe opposed narrow ends. The housing is longer than conventional presentday housings. End bosses 12 designated 12L and 12R of different heights,cooperate with complementary lid 17 shapes, not shown, to ensure thatthe lid may only be applied one way.

Most of the elements and features shown, with the notable exception, ofthe trough line, are equally useful with a square housing.

It is convenient herein to refer to the `left` and `right` ends of thehousing, to its `top` and `bottom` and to the `near` and `far` sides.This refers to the orientation of FIG. 3 and is only for convenience ofdescription and in actual use the designation left, right, near, faretc. may not describe the actual physical locations or directions.

At the left hand end of the housing there is a common port CP and apedestal port PP. At the opposite end of the housing there is an aerialport AP. At each of these ports, a boss 18 with threading (not shown)receives a connector which has complementary threading designed tomechanically and electrically connect the outside conductor of thecoaxial distribution cable to the housing which is electricallyconducting.

By `coaxial cable` herein, unless otherwise specially qualified I meanthe distribution coaxial cable or `hard line` which extends between`multitap` housings. By `multitaps` I mean a housing similar orperforming a similar function to the one described herein, whichdistributes a small fraction of the RF signal to individual cablesubscribers on `drop` lines from secondary or tap ports which receivethe output of the splitter in the housing. FIG. 1 shows an aerialmounting for the housing and FIG. 2 a pedestal mounting. Eight tap ports22, without drop lines attached are shown in FIGS. 1 and 2.

In accord with conventional coaxial cable design, a pin, electricallyconnected to the center conductor of the cable, projects beyond thefitting of the outer conductor and on connection of the outer conductorto the housing, the pin will project through the end wall of the housingfor connection to the circuitry therein. Many variants of such pins areknown in the CATV industry and in some cases the pin may be part of anextension fitting which connects to the central conductor proper. Allsuch pins, forming an electrical extension of the central conductorproper should operate with the invention described herein.

FIG. 1 shows a housing `aerial mounted` on a line 24 with coaxial cable26 connected at port CP and at port AP. It will be noted that the portPP is not in use.

FIG. 2 shows a housing `pedestal mounted` on a frame 28 with coaxialcable 26 connected to ports CP and PP. It will be noted that the port APis not in use.

Not shown in FIGS. 1 and 2 are the drop lines which would normally beconnected to the tap ports 22.

By RF signal direction along a line 26 or through a housing 10 I meanthe direction of the main RF signal which is of much higher frequencythan any reverse RF signal. AC power is frequently also carried on thecable 26.

RF signal direction may be in either direction through the housingsdescribed herein.

In the housing of FIG. 3 are four bosses 12 for lid attachment by bolts26. (See also FIGS. 1 and 2) 12L and 12R are differently raised so thehousing must be put on the right way. Centrally of the housing is mainboss 30 for attachment of the housing to an aerial or pedestal mountingbracket.

A platform comprising generally rectangular first insulating plate 32(commonly called a motherboard) with attached internal transmission line(called herein a trough line 34) is adapted for mounting on the housingby bolts in platform bosses PB1-PB8 numbered clockwise (FIG. 4) and PB9.The motherboard and trough line are preferably a permanently connectedunit and fastened to the platform bosses by bolts and the platform ispreferably therefore attachable or removeable as a unit.

On opposite sides of the left edge of motherboard 32 are the terminals38C and 38P (FIGS. 1, 2, 6 and 7).

As noted the motherboard 32 is cut away at its left hand corners,adjacent the CP and PP ports, (FIGS. 3 and 4) so that it may, asdescribed hereafter, be lifted upward out of the housing from below toabove the respective inwardly projecting coaxial cable pin P2 (FIG. 4).For mounting the terminals 38C or 38P on the board 32 there is providedan inverted U-shaped conducting bracket 42L which has downwardlyextending tabs 44 for attachment to the board and electrical connectionto the RF through line to be described. The side walls 46-57 of eachbracket (as shown in FIGS. 9A, 9B) are provided with four downwardlyprojecting legs which are provided at their free ends with ends 44 bentin end section to be clipped into apertures in the motherboard. Solderis used on the underside of the motherboard to otherwise fix the bracket42L (FIG. 9A) in place thereon. (Other modes of attachment may be used.)Foil 48 (FIG. 5) on the underside of the motherboard electricallyconnects bracket 42L with a capacitor 50 and with AC coil 64. Thebracket 42L is dimensioned to project leftwardly of the motherboard tostraddle the entrance axis E (FIGS. 8C and 9A) of the pin with one (herethe inside) of the bracket walls extending leftward beyond the other toprovide at its leftward end an outward (relative to the other wall inhorizontal section) a guide surface 52 shaped to tend to guide anentering pin toward the other bracket wall. A leftward extending clip 54has in horizontal section, (FIGS. 12A-12C) a wall 55 fastened to theoutside of wall 57, a hairpin turn at its rightward end and a resilientfree clip wall 56 extending generally toward the pin and, in its reststate, sloping inwardly to overlap the pin entrance point. The leftwardend of the clip wall is shaped in horizontal section to form a guidesurface 58 sloping away from the guide surface 52. The right handbracket 38A (see FIGS. 8A-8C) is identical to 38C and 38P except that itomits attachment tabs 44.

The result is that an entering pin P2 comes in contact with the guidesurfaces 52, 58 and deflects the clip wall 56 from its rest position toallow the pin P2 to make good electrical contact with clip 56 and wall57. If the pin is withdrawn the clip returns to its rest position. Onlyone of the interacting clip and bracket wall need be a conductor butmore certain electrical contact is made if both are. Thus clip 56 andwall 57 act as the terminal's electrical contacts.

It will be noted therefore that the pin P2 with its coaxial connectormay be attached to and detached from the mechanical and electricalconnection to the terminal, without any movement of the bracket orindeed the necessity of opening the casing.

It will be noted that surfaces of the clip 56 and wall 57 extendgenerally perpendicular to the motherboard in areas adjacent theircontact with the pin. This perpendicularity is designed, in combinationwith the spreader means to be described, to allow vertical removal andattachment of the clip and contact wall into and out of contact with pinP2, without the necessity of removing or adjusting the coaxial cable andpin P2.

In the cross bar of a U-shaped bracket 42R or 42L, there is provided, akey 60 rotatably mounted to rotate about a vertical axis. The key isdesigned to include a vane 62 and guide edge 63. When the clip 56 is inrest position (FIG. 12C) or resiliently deflected by the pin (FIG. 12B),the guide edge and vane extend parallel to wall 57), in inoperableposition. When it is desired to deflect the clip 56 to a spacing fromthe bracket wall 46 wider than the pin P2 diameter, the vane is rotatedby the key handle and is designed to frictionally engage the clip 56surface to hold it in spread position. With the clip 56 in spreadposition, the terminal 38 may be moved vertically to or from itsposition straddling a pin P2. With the platform comprising motherboardand trough line as shown in FIG. 12, there will be terminals 38 at theCP, AP, and PP ports and that of the CP terminal and of one of theothers, will be in use. With such two terminals engaged to pins P2, themotherboard-trough line platform may be lifted vertically out of thehousing, or inserted vertically into the housing with the two terminalscorresponding to pins P2 to straddle the pin, without the necessity ofremoving or otherwise disturbing the pin and coaxial cable attachmentsat the respective ports. The use of the key is proposed for both removaland attachment. However it is within the scope of the invention tomerely slide the terminal contacts off the pin when removing them and touse the spreader key when placing the contacts in straddling positionwhen applying them.

Moreover it is within the scope of the invention to provide the loweredges of clip 56 and wall 57 with downwardly diverging guide surfaceswhich will allow a terminal 38 to be moved downwardly into contact witha pin P2, and be spread by the pin itself so that, in the latter design,the key 60 is not required to spread the contacts.

Wall 57 is preferably provided with a tab 61 bent to project toward clip56 and, in the absence of a pin to retain clip 56 at less than pinspacing but under slight bending stress to avoid its casual movement.

Other terminals than the preferred terminal, just described may be used.Such other terminals will preferably allows vertical removal of theterminal from the housing; permanent mechanical connection to themotherboard; and permanent electrical connection to the RF path.

Wall 57 is preferably provided with a tab 61 bent to project toward clip56 and, in the absence of a pin to retain clip 56 at less than pinspacing but under slight bending stress to avoid its casual movement.

The motherboard 32 also referred to as the first insulator plate, is ofgenerally rectangular form and occupies the housing to the left of mainboss 30. The motherboard is cut away at the two left corners to clearpins P2 at ports CP and PP and with a rectangular cut out on the leftside facing the left housing wall between platform bosses PB1 and PB8. Acentral, short, rectangular extension 112 on the right hand edge of themotherboard is located to support the splitter interface 65 (FIG. 3).The motherboard must be of relatively thin insulating materialpreferably of epoxy resin and glass fibre but may be made of otherinsulating materials. The material of the motherboard will cause signallosses in the RF circuit. Expense must be balanced against RF losses inthe selection of such insulating materials. As shown, the motherboardwill be mounted on platform bosses PB1, PB2, PB7, PB8 by bolts, notshown, bolted into the bosses.

The circuitry and components are provided as in FIGS. 5-7 and 18 whichshow the top of the motherboard. The terminal 38C is electricallyconnected through capacitor C1 (FIG. 6) to daughter board probe DB1 byfoil conducting extent F1 on the bottom of the motherboard. The daughterboard 67 is a second plate of insulating material and will usually bethe same material as the motherboard. All foil conducting extents are onthe bottom of the motherboard. Daughter board probe DB1 is, ashereinafter described, connected to probe DB7 through the couplercircuit on the daughter board, to be described later, or through thebypass BP, determined as hereinafter described. Bypass BP is at itsother end connected daughter board probe DB7. (Daughter board probes DB1to DB7 are mounted on the motherboard and will act to mechanically mountthe daughter board thereon and to electrically respectively connect todaughter board sockets DS1-DS7. (If the daughter board is reversedrelative to the motherboard because of a reversal of RF signal path thenprobes DB1-PB7 will be respectively connected to daughter board socketsDS7-DS1.)

Probe PB7 is connected along foil extent F2 to condenser C2 whose otherside is connected to fixed terminal A of the transfer switch TS.

The AC circuit is connected from the bracket 38C to one side of thepower coil 64 whose other side is connected to foil extent F3 which isin turn connected to terminal A of the transfer switch TS. The powercoil may also be permanently connected to terminal A.

The transfer switch has also terminal B connected to the centralconductor 122 of the trough line T1, and the other end is connected tothe terminal at port AP.

Terminal C of the transfer switch is connected to the housing at bossPB7 through resistor R4. The connection of resistor R4 to boss PB7 maybe through ground plane GP1, as shown in FIGS. 6 and 7 or alternativelythrough the outer conductor of trough line 34. Resistor R4 is of thecharacteristic resistance between the coaxial distribution cable 26inner and outer conductors, usually 75 ohms.

Terminal D of the transfer switch is connected to the terminal 38P atport PP.

Thus the RF circuit over the motherboard is from CP terminal 38P, acrosscondenser C1 over foil extent F1, to daughter board probe DB1. From DB1to DB7 the RF circuit may go through the directional coupler on thedaughter board to DB7 or may go to DB7 through the bypass BP. From DB7the RF circuit goes over F2, C2 and F3 to terminal A. The RF signal maygo across the motherboard in the opposite direction in which case thedaughter board connections are reversed so that DB1 is connected todaughter board socket DS7 and so on.

The AC coil connects to terminal 38C and to terminal A. The AC coil isselected relative to the RF path to allow only a controllable proportion(usually small) of the AC power coming in on the distribution cable tobe delivered to the directional coupler circuit. If desired forachieving a different proportion capacitors C1 and C2 may be omitted.However if C1 or C2 is omitted, then a capacitor should be placed inbypass circuit BP. In the absence of C1 or C2 the added capacitor willavoid the shorting out of the AC power coil by the bypass, whenconnected.

The rotary transfer switch TS is a two position switch havingdiametrically opposed connector bars. In one position (when aerial portAP is used) bar B2 will connect terminals A and B and the bar B2 willconnect terminals C and D. In the other position (when the pedestal portis used) bar B2 will connect terminals D and A and the other bar willconnect terminals B and C.

An elevated conductor C6 may be used as shown in FIG. 23, between nodesN1 and N2 or N3 and N4 (FIG. 5). The elevated conductor provides an airbarrier below and greatly reduces the dissipation of signal losses inthe motherboard. The elevated conductor may be used with or without acondenser in the line. If the elevated conductor is used, the connectorto the power coil may be soldered thereto, on the daughter board remoteside of the condenser is used. An elevated conductor C1 may be used inplace of any foil connected part of the RF circuit.

The daughter board mount 72 is an insulating block attached to the uppersurface of the motherboard in any desired manner. The daughter boardmount provides the seven upwardly projecting daughter board probes,numbered DB1 to DB7. The daughter board provides seven complementarydownwardly facing sockets DS 1 to DS 7 in a downwardly open recess 74preferably defined by the daughter board insulating material.

The daughter board material is a somewhat lossy insulating materialsimilar to the motherboard and preferably is glass fibre insulatingmaterial similar to the motherboard.

FIG. 16 schematically illustrates the directional coupler circuit on thedaughter board. The conductors shown on the front of the daughter boardare preferably made of foil. Thus DS1 is electrically connected by line102 to the input coil of a voltage transformer 78. The coil's other endis connected to DS7. DS2 is grounded on the motherboard and is connectedto one side of the input coil of a current transformer 80 and the otherside of the input coil of a current transformer 80 and the other side ofinput coil of current transformer 80 is in series with the input coil ofvoltage transformer 78.

Socket DS3 is connected in series with the secondary of currenttransformer 80, a resistor R2 splitter node N6, the secondary of voltagetransformer 78 to socket DS5. Socket DS3 is also connected to pin DS5.The splitter node N6 is connected to pin DS5. In operation thetransformers are wired in a sense to give the desired splitter voltageat node N6 when the RF signal input is applied at DS1 (the main feedinput terminal) and the RF signal output goes out over socket DS7 (themain feed output terminal). If the RF signal were input at DS7 andoutput at DS1 the splitter signal at splitter node N6 would be of nouseful value Hence if the RF signal were toward rather than away fromthe CP terminal the daughter board must be reversed relative to themotherboard.

Thus, before reversal, with the RF signal coming from the common port CPthe splitter will be oriented as shown in FIG. 16 and probes DB1-DB7connected respectively to DS1 to DS7. After reversal with the signalgoing to the common port CP the daughter board is reversed from thatshown and probes DB1-DB7 connected respectively to DS7 to DS1 so thatthe coupler input signal is travelling into the coupler circuit from DS7to DS1 and the coupler output signal is travelling out of the couplercircuit from DS7 to DB1. It will be noted that in either position DB4 isconnected to DS4 to carry the splitter output of the coupler circuitalong line 82 to the splitter interface central conductor terminal 90 onthe motherboard.

The daughter board on the other side forms the circuitry described withfoil within the bounds of dotted lines 85 behind the lines from DS1 andDS2, behind the line from DS7 and behind the line containing node N5 andthe input of voltage transformer 78. The foil within dotted line 84' isconnected to daughter board sockets DS2 and DS6.

(In FIG. 5 the view is from the top of the motherboard. However in thisFigure only the components on the top of the motherboard are shown inchain dots and the foil on the bottom of the motherboard is shownsolid.)

With the foil on the back of the daughter board, connected to terminalsDS2 and DS6, these are connected respectively to DB2 and DB6 for RFsignal from port CP; or respectively connected to DB6 and DB2 for RFsignal to port CP.

FIGS. 5, 6 and 7 show that DB2 and DB6 are connected by foil on the backof the motherboard. The foil patterns on the back of the motherboardhave RF path connections shaded as sloping upward and to the left andground connections shaded to slope upward and to the right. The RF pathconnections have been elsewhere discussed.

The ground planes are two. Ground plane GP1 is connected to platformbosses PB-8 and PB-1 and approaches closely to the RF paths to or fromterminals 38 at the CP and PP ports. The edge of GP1 closely accompaniesthe RF path between PB1 and daughter board probe DB2 and the RF pathbetween DB6 and C2, on both sides, with a strip going to ground at bossPB7. From PB7 the edge of GP1 accompanies the RF path between transferswitch terminal B, toward transfer switch terminal A and curves over toform an edge adjacent the RF terminal at the pedestal port and to groundat PB-8. The ground plate GP1 has provided what might be called a`ground current path` closely spaced from substantial extents of the RFpath and an approximate attempt is made to approximate thecharacteristic resistance, usually 75 ohms, between these points. Thusthe ground plane GP1 acts in the place of the outer conductor of atransmission line and `organizes` the ground currents accordingly. Thisreduces the effects of housing: standing waves summation and reflectionson the RF path and obviates the necessity of a coaxial cable inside thehousing, so that the terminals 38 may be directly connected to coaxialcable pins at the CP and AP ports. The ground plane GP1 shields andlessens the effect of the ground currents associated with the RF linefrom those associated with the coupler both in the vicinity of thedaughter board support and between the transfer switch and the splitterinterface terminal 62. Lessening the effect of RF through line signalson the coupler and splitter signals is of considerable importance sincesubstantial attentuation of the coupler and splitter signals, relativeto the RF through path signals, means that in case of interaction of thesignals, the latter may seriously affect the quality of the former.

Ground plane GP2 also of conducting foil on the bottom of themotherboard further contributes to the isolation of the coupler outputalong foil line 84. Ground plane GP2 includes a path between probes DB3and DB5 which passes between probes DB4, the coupler output and GP1.Thus the ground currents on GP1 and GP2 may slightly interact but eachprotects a signal path. GP1 protects the signals on the RF through pathand GP2 protects the coupler output. Accordingly GP2 includes an edge90' (FIG. 7) facing the coupler path 84 between probe DB4 and thecentral conductor 90 at the splitter interface. Edge 90' defines theground plane GP2 and is grounded at platform boss PB2. GP2 has extents92 and 94 located on each side of splitter interface terminal 90 and aremechanically shaped and mounted on the motherboard to make connectionwith the outer conductor 65 of the splitter interface. Again the groundplane GP2 is located to follow the coupler signal from probe DB4 to thesplitter interface conductor 90 with the characteristic impedancetherebetween but connects to the outer conductor 65 of the interfacethus the ground currents in GP2 adjacent conductor 90 and the splittercentral conductor have impedance approximately of the characteristicvalue therebetween, but the splitter central and outside conductors willrespectively connect their splitter signals and ground currentconnections in a similar relationship to grounding connections andsignal destinations in the splitter.

The ground currents in ground planes GP1 and GP2 are connected to thehousing where shown. Because the currents in the ground planes followtheir respective signal paths the consequential currents in the housingand its impedances and potential standing waves have a much lessenedeffect on the RF through line or coupler signal paths than with priordevices.

Connections from the ground planes to the housing are preferably made atintervals less than half the wavelength of the highest RF frequencyencountered so that harmonics and standing waves arising in the housingwill not have significant interaction with the RF signals.

It has sometimes been found that losses due to standing wave interactionare reduced if GP1 and GP2 are connected over the semicircular arc TZshown in FIGS. 5, 6 and 7, as separating them. Even with such connectionat TZ, currents over TZ do not substantially interfere with the abilityof GP1 and GP2 to interact with the respective (through and splitterinterface) signal paths.

As noted a bypass circuit is provided to maintain the signal path on theRF through line when the daughter board is removed. This maintainsservice to `downstream` housings and subscribers at times when thedaughter board is removed for repair or replacement. Spring connectors90 and 92 are electrically connected by bypass BP.

Mounted on the motherboard is the daughter board bracket 72. Extendingthrough the motherboard and connected by solder thereto are upstandingflat spring connectors 90 and 92 each mounted outwardly of the daughterboard probes DB1 and DB7 and bent in the direction permitted by thesprings' flatwise shape, to achieve contact with respective daughterboard probes DB1 and DB7 in the absence of the daughter board. Thesloping spring ends 94 and 96 are also designed to be deflected out ofcontact with their respective probes by the daughter board socket wall98 when in the downward location of the daughter board.

It is of some importance to note that, preferably, the connection ofprobes DB1 and DB7 (and preferably the rest of the probes) with thecorresponding daughter board sockets takes place at a higher point inthe relative travel of the daughter board relative to the motherboard,than the connect-disconnect point between the probes and the flatsprings. Thus FIG. 14 shows the daughter board probes DB1-DB7 fullyinserted in daughter board sockets DS1-DS7. Thus in FIG. 14, it is notedthat the socket wall 98 maintains spring ends 94 and 96 out ofelectrical contact with probes DB1 and DB7, respectively.

On the other hand, FIG. 13 shows the daughter board displaced from fullyassembled position to a relative location where wall 98 has allowedspring ends 94 and 96 to make respective electrical contact with probesDB1 and DB7 while the DB probes are each in contact with thecorresponding DS sockets.

Thus when the daughter board sockets fully receive the motherboardprobes (FIG. 14) the spring contacts 92 and 94 are disconnected from themotherboard probes and the bypass BP is therefore open. The RF throughpath between foil extent F1 and foil extent F2, is connected throughlines 102 and 104 of the coupler circuit (FIG. 16).

As the daughter board is progressively raised relative to themotherboard probes FIGS. 13, 14, 15A and 15C the spring contacts firstcontact the daughter board probes DB1 and DB7 (FIG. 3) and the bypass BPis connected between F1 and F2 before connection is broken to thedaughter board forks. At a higher level the sockets DS1-DS7 disconnectfrom the daughter board probes DB1-DB7. The RF through line between theCP terminal and the transfer switch terminal A is then completed overthe bypass BP before the connection over the coupler lines 102 and 104is broken.

If the daughter board or its replacement is then lowered into position,the daughter board sockets are first connected to the motherboard probes(FIG. 13) and later the spring bypass member 94 and 96 are disconnected.The RF through line is thus connected over the coupler input circuitlines 102 and 104 FIG. 16 before the bypass BP disconnected. Thusremoval or replacement of the daughter board was achieved withoutinterrupting the RF through path to downstream equipment or subscribers.

Thus on either the connection or disconnection of the daughter boardbetween the terminal and the transfer switch, one of the alternateconnections between these points is completed before the other isbroken. This make-before-break mode of operation acts to maintainthrough RF service to the downstream users of the RF during connection,disconnection of and the existence of the disconnected state of thedaughter board. Thus the work on the subject equipment does notinterrupt the service to downstream subscribers.

The make-before-break quality of the switch bypass circuitry renders itvaluable, not only with the circuitry and components described hereinbut in other circuits where: a disconnectable component and an RF lineand a potential bypass therefore while it is disconnected, are provided.

The line 106 to one end of the power coil is connected to node N1 andhence to the CP terminal. The line 108 from the other end of the powercoil is connected to node N4 and hence to terminal A of the transferswitch and to probe 7 of the daughter board mounting block. The ends ofthe lines are customarily soldered or welded to the respective nodes N7,N8.

If the RF lines N3 to N4 and N1 to N2 are provided with capacitors (C1and C2) the power coil lines are connected to the lines N3-N4 and N1-N2on the sides of the capacitors C1 or C2 remote from the daughter board.

The AC coil by its nature (primarily its high inductance) and by itsdesign, allows only a negligible amount of RF from the RF through lineto pass through. The coupler circuit by its nature and design isarranged to allow only a small and controllable amount of AC powerthrough the coupler circuit. If there is a risk that too much AC willreach the coupler circuit then capacitors C1 and C2 with a very highimpedance to AC may be used. It is noted that if capacitors C1 and C2are not used in the connections between N1-N2 and N3-N4 then the bypasscircuit when connected will short out the power coil. Thus a capacitor(not shown) in line BP will be required to avoid this.

The splitter interface circuit 112 is mounted on the motherboard and itscentral conductor connection 90 appears herein as an anchor point inFIGS. 5,6,7 connectable to the central conductor to the splitter whilethe four raised walls 65 (FIG. 3) are conducting connectable as theouter conductor of the interface for connection to the outer conductorof the splitter (not shown). Thus splitter center conductor connectionpoint 90 is connected by foil 84 on the back of the motherboard (FIG. 5)to the probe DB4 of the daughter board bracket and is not connected tothe ground plane GP2. However the outer conductor 65 is connected atanchor points 118, to the ground plane GP2. As previously noted theground plane GP2 edge is contoured relative to the foil conductor 84from probe DB4 (and on both sides thereof) to the splitter connectionpoint 90 to provide approximately the characteristic impedance betweenGP2 and conductor 84.

GP2 is connected to the housing at PB2. GP2 may also be connected to GP1where the motherboard at the daughter board connection to control groundplane resources.

The foil of GP2 thus provides a conductor for ground currentconsequential on the RF coupler output signal on conducting path 84,approaching the effect of having an outer `coaxial` conductor for path84. Excitation of unwanted currents in the housing is thus greatlyreduced and signal strength less attenuated. The coupler output on path84 is also shielded by GP2 from large effects due to RF signals on theRF through path.

The splitter (not described herein) is designed to provide an outerconductor 65 connectable to a similar outer conductor on the splitterand there will be a central splitter conductor to the splitter anchorpoint to carry the RF signal at 90 from the coupler output to thesplitter input. The splitter and its connection to the secondary or `F`taps are not further described herein as these may be provided in manyforms well known to those skilled in the art. The splitter interfacecircuit may be embodied in other ways easily available to those skilledin the art. The relationship of GP2 to path 84 from the coupler tapoutput to splitter interface central conductor 90 is part of a facet ofthis invention.

The transfer switch (FIG. 6, 7, and 17-20) comprises four stationaryterminals A, B, C, D lettered clockwise and at 90° azimuth angles abouttheir centre. Terminal A is connected to F3 and the RF circuit as beforedescribed. Terminal B in the long housing is connected to the centralconductor of an air line 122, to be described. (In the short housingwhich is of a more square shape terminal B will be connected to theaerial terminal as previously noted).

Terminal C is connected to the outer connection of the air line througha resistor R4 (FIG. 5) having the characteristic impedance of the airline. Terminal D is connected to the terminal 38P for port PP at anchorpoint 127 (FIG. 6).

As will be noted from FIGS. 17-20 each of terminals A, B, C, D isseparately anchored to the motherboard. Terminals A, B, C, and D arespaced from the RF ground plane GP1. Terminal C is of course connectedthereto through resistor R4 (FIGS. 5 and 6).

The RF ground plane GP1 is connected to both the inside and outsidesurfaces of outer air line conductor 124 at 126.

The rotary transfer switch is provided with a keying slot 130 (FIG. 7)so that the transfer switch may be operated by a suitable tool. Theswitch is also provided with a split spline which is grooved at 132(FIG. 18) to be snapped into and receive the motherboard. The transferswitch has two positions and is provided with parallel opposedconducting bars 134 B1 and B2 (FIGS. 6, 19 and 20) on its lower side toconnect respective contacts joining opposite sides of the square definedby A, B, C, D. Thus with reversible 90° rotations (set by click-overmechanism, not shown) the switch will connect A to B and C to D at oneposition and connect D to A and B to C at the other position. In theFIG. 20, the switch is connecting A (the power coil and RF throughcircuit) to the centre conductor 122 of the trough line and (C to D) theterminal 38P of pedestal port PP to resistance R4 to ground. Theconnection to ground is shown as through ground plane GP1 from node N9to the adjacent housing connection PB7 (FIG. 5).

The air line or trough line outer conductor 124 is preferably in theform of an inverted U and may be cut away as at 123 (FIG. 21) formounting purposes. The outer conductor is mounted on the housing bybolts, preferably at points spaced less than 1/2 the wavelength at thehighest RF frequency encountered to reduce the risk of effect, of thegeneration in the housing or air line of standing waves or harmonics, onthe signal transmitted along the central conductor or surface of 124.The outer conductor 124 is also connected to the RF ground plane at:PB4, PB5, PB6, PB7, PB9--see FIG. 7.

The central conductor 122 of the air line is preferably of the shape ofa flat bar and substantially parallel to the side walls of outerconductor 124 along its length (FIGS. 21, 22, 10A and 10B). Outerconductor 124 and inner conductor 122 are oriented so that their freeend edges face the bottom housing wall (FIG. 10B). These could equallywell face the adjacent side housing wall. The transmission line justdescribed and herein preferred is often known as a trough line.

(Another transmission line shape could be used. For example the ordinarycoaxial conductor could be used. However more losses could beencountered because solid lossy dielectric supports of the centralconductor cause more losses in the RF signal than with the `airdielectric` available with the trough line). For other variants orpossible transmission lines which could be used, see for example`Microwave Engineering` by A. F. Harvey, Academic Press, London and NewYork.

In the preferred air line in accord with the invention the outerconductor is inverted with its edges directed downwardly to have minimalRF interaction with the splitter circuit (not shown) but which will bemounted on the lid of the housing. The outer conductor is connected tothe housing at bosses (FIG. 7) spaced at less than 1/2 wavelength of thehighest frequency for which the system is designed. The outer air lineconductor 124, adjacent the AP port is provided with an out-turnedflange 134 (FIGS. 10A, 4) arranged to be spaced from the bottom wall ofthe housing. The out-turned flange is apertured as shown. Adjacent thisarea, is boss PB5.

A plastic block 139 (FIG. 10A) is provided apertured at one side to seatabout boss PB5 and provided with a surface to support the out-turnedflange 134 whose aperture also receives the boss PB5.

The plastic block 139 extends below the out-turned flange to a locationbelow the inner and outer conductors. Parallel grooves 142 are locatedin the plastic block, which receives the downward facing edges of theterminal bracket 38A which is in the form of FIG. 8C and thus supportthe inner conductor, which at its right hand end is welded to the sidewall of terminal bracket 38A. Also adjacent the right hand end a plasticpeg 144 is snapped into the side wall of outer conductor 124, as shownand receives the inner conductor 122 as a snap fit in its jaws 146. Theleft hand end of the inner conductor is attached to the motherboard(FIG. 22) and shaped to form terminal B of the transfer switch. (FIGS.19 and 20). The outer conductor 124 is attached to the motherboard (FIG.22). At the motherboard, conductors 122 and 124 are shown as connectedto different electrical circuits, (FIG. 5). Conductor 122 continues theRF circuit from terminal B (if connected) to terminal 38A to which it iswelded Conductor 124 is connected at node N9 to GP1. It is noted thatboth the inside surface and the outside surface of outer conductor 124are connected to GP1.

A second plastic peg 144 (FIG. 21) may connect the central and outerconductors near the motherboard although this may be thoughtunnecessary.

It will thus be seen that an air dielectric is provided between theinner and outer air line conductors 122 and 124 between the end supportsfor inner conductor 122 at plastic block 139.

With the long housing then, the motherboard 32 and trough line 122, 124form a physically unitary platform which may be lifted out and into thehousing as a unit, and without disconnecting or touching the coaxialcable connections. To remove the platform the following steps occur. Thetwo terminals in use (FIG. 7) will be CP terminal 38C and AP terminal38A (aerial connection) or CP terminal 38C and PP terminal 38P (pedestalconnection). The keys (FIG. 11A-12C) for the terminals in use are turnedto move the clip 56 in each out of seizure of the coaxial cable pin. Thebolts for platform bosses PB1-PB9 are removed. The platform may then besimply lifted out.

To attach a platform, comprising motherboard 32 and trough line 122, 124in the housing, the relevant terminals 38C and one of 38A or 38P arespread by key 60 so that the contact surfaces are spread wider than thecorresponding coaxial cable pins P2 and the platform set in place sothat the contact surfaces 56, 57 straddle the relevant coaxial cablepins P2. The platform is then mounted by inserting the bolts in theplatform mounting bosses PB1-PB9. With the platform bolted in place, thespreader keys are rotated to inactive position allowing the contactsurface of the contact members 57, 58 to seize the pins.

It will be noted that, a platform may be mounted in the housing, orwithdrawn from and replaced in the housing without the necessity ofdisconnecting the coaxial cables and pins.

With a platform in place, if it is desired to remove an attached coaxialcable, it is merely necessary to screw off the exterior conductorattachment, as is well known in the art, and withdraw the coaxial cable.The coaxial pin slides out from between the contact surfaces 57, 58which, under their bias move to rest position, as shown in FIG. 11C.

If it is desired to attach a coaxial cable, with the platform in place,the exterior conductor of the coaxial cable is attached in a manner wellknown to those skilled in the art, drawing the projecting pin inside thehousing wall. The entering pin separates the contact guide surfaces ofmembers 56, 57 against the bias of clip 56 and establishes electricalcontact therewith.

It will be noted that, disconnection of a coaxial cable from orconnection of a coaxial cable to the housing, may be performed withoutany manipulation of the platform and, indeed, without removing the lid17 from housing.

If it is desired to convert a housing from use in a pedestal mounting touse in an aerial mounting, the coaxial cable is detached from ports PPand CP and the housing from the pedestal frame 28. The transfer switchis changed from its setting connecting terminals D-A to that connectingports A-B (FIGS. 19 and 20). The housing may then be mounted on itsaerial mount and coaxial cables attached at ports AP and CP.

To convert a housing from use in an aerial to use in a pedestal mount,the above procedure is reversed.

If, whether intended for pedestal or aerial mounting, the RF signaldirection along the RF through line is reversed, the daughter boardcontaining the coupler circuit is reversed so that the former daughterboard connection DS1-DS7 to respectively DB1-DB7, is reversed, so thatDS7-DS1 is respectively connected to DB1-DB7. It will be noted that thisis the only change which need be made, the coupler output from DB4 tosplitter interface terminal 90 being unchanged for either orientation ofthe daughter board. No change need be made in the motherboard orin-housing transmission (trough) line 122, 124 and, on the subscriber'sside, (not shown) no change need be made in the splitter or secondarytap circuitry.

Where it is desired to use a shorter housing this will assume agenerally square shape and the in-housing transmission line will beeliminated and the aerial port terminal placed on the motherboard andconnected directly to transfer switch terminal B.

The shielding and ground current management is reviewed as follows: AnRF signal entering the housing at pin P2 at the common port CP entersthe housing at terminal 38C and travels as described to probe DB1. Theouter conductor of the coaxial cable accompanying P1 is electrically(and mechanically) connected to the housing at port CP. Ground plate GP1is grounded to the housing at PB1 (as close to port CP as practical) forminimum housing conduction of the ground current. Edge E1 of GP1 thus`accompanies` closely the RF path to the daughter board probe DB2. Ifthe daughter board is in place, the RF signal at probe DB1, travels onlines 102 and 104 to probe DB7. The RF signal on the daughter board isaccompanied by foil 85 which accompanies lines 102 and 104 and foil 85connects probes DB2 and DB6. Thus the RF signal to probe DB7 isaccompanied by foil 85 which forms a continuation of GP1 across thedaughter board. (It is noted that, at the same time edge E2 of GP1 isspaced from edge C2 of ground plane GP2). As the RF signal exits thedaughter board probe at DB7, edge E3 of GP1 accompanies foil F2. Foil ofGP1 accompanies the RF path from C2 paralleling F3 to transfer switchpaths A-B to connect to trough line outer conductor 124 and from thereto aerial port AP where the conductor 124 connects to the housing at PB5which is as close as practical to the connection between the AP outerconductor of the coaxial cable and the housing. Thus an RF signal fromport CP to port AP is accompanied by a ground current path over GP1 andconductor 124.

Another limb of GP1 connects at PB1 as closely as practical to thehousing where an outer cable would be connected at port PP.

Thus the ground plane acts as an extension of the outer distributionconductors connected at CP and AP or CP and PP. The impedance betweenthe RF signal path and its accompanying portion or edge of ground planeGP1 may be as close to the characteristic impedance to reduce RF signallosses. The ground plane GP1 thus reduces the interaction between the RFsignal and the housing.

The interaction of the RF signal with the housing is further reduced bymaintaining the housing lengths where the housing does form a part ofthe ground current path as short as possible. Such housing lengths are:From the distribution cable outer conductor at port CP to PB1, from anouter conductor at PP to PB8 and from the outer conductor at AP to PB5.

The above benefits hold true if the RF path so the signal is going fromAP or PP to CP, with the daughter board reversed.

The ground plane GP1 also shields the currents in the coupler splitterpath 84 from signals on the through path.

Ground plane GP2 similarly accompanies the path at approximatelycharacteristic impedance thereto from probe DB4 to splitter interfaceterminal 90. GP2 similarly continues the ground current path at (about)the characteristic impedance from the daughter board circuit over probesDB3 and DB5 to nodes 118 where they connect to the outer conductor 65 ofthe splitter interface to continue the ground current path. GP2 is alsoconnected to the housing at PB2, and may be joined to GP1 on themotherboard adjacent the motherboard socket to dissipate standing waveswhich tend to form on the foil, ground planes.

I claim:
 1. In combination a first RF circuit extending between ends,said circuit including a first and a second contact,said first andsecond contacts being spaced from each other and defining a gap in saidcircuit, a second RF circuit having a third contact connectable to oneof said first and second contacts and a fourth contact connectable tothe other of said first and second contacts, fifth contact connectableto one of said first and second contacts and a sixth contact connectableto the other of said first and second contacts, means responsive torelative movement of said third and fourth contacts to establishrespective connections with said first and second contacts to thereafterbreak the connection of said first and second contacts from said thirdand fourth contacts, means responsive to relative movement of said thirdand fourth contacts to break the connections with said first and secondcontacts, to therebefore establish the connections of said fifth andsixth contacts with said first and second contacts.
 2. A combination asclaimed in claim 1 wherein said first RF circuit is mounted on aninsulating plate.
 3. A combination as claimed in claim 2 wherein saidsecond RF circuit connects said first and second contacts when saidthird and fourth contacts are each connected to one of said first andsecond contacts.
 4. A combination as claimed in claim 2 wherein saidfifth and sixth contacts are mounted on said insulating plate and areconnected by a conductor to connect said first and second contacts wheneach is in contact with one of said first and second contacts.
 5. Acombination as claimed in claim 3 wherein said fifth and sixth contactsare mounted on said insulating plate and are connected by a conductor toconnect said first and second contacts when each is in contact with oneof said first and second contacts.
 6. A combination as claimed in claim1 wherein said second RF comprises a coupler.
 7. A combination asclaimed in claim 2 wherein said second RF comprises a coupler.
 8. Acombination as claimed in claim 3 wherein said second RF comprises acoupler.
 9. In combination an insulated plate constructed to be mountedin a coaxial cable housing,means defining a first RF path on said plate,a pair of spaced conducting probes mounted to project from said plate,said probes defining a gap in said first RF path, moveable meansmounting a second RF path extending between a pair of conductingsockets, said sockets being shaped to respectively receive said probesin respective conducting relationship, said moveable means movingbetween a first position where said sockets respectively receive saidprobes and a second position where said sockets are respectivelydisconnected from said probes, a pair of contacts moveably mounted onsaid plate connected by an RF bypass circuit, each contact beingdisconnectably connectable to a different one of said probes, meansresponsive to movement of said moveable means from said first towardsaid second position to connect said contacts to said probes before thedisconnection of said probes from said sockets, means responsive tomovement of said moveable means from said second toward said firstposition to connect said sockets to said probes before the disconnectionof said contacts from said probes.
 10. A combination, as claimed inclaim 9 wherein said contacts are spring clips, normally biased intocontact with respective probes and deflectable by said movable means onits approach.
 11. A combination as claimed in claim 9 wherein saidmoveable means carries a coupler circuit including said second RF path.12. A combination, as claimed in claim 10 wherein said moveable meanscarries a coupler circuit including said second RF path.
 13. Acombination as claimed in claim 9 wherein each socket will receiveeither probe.
 14. A combination as claimed in claim 11 wherein eachsocket will receive either probe.